1. Field of the Invention
This invention relates generally to devices for implanting a medical ventilation tube through a thin membrane of a person, and particularly to a method and apparatus for implanting an otological ventilation tube through the tympanic membrane in which the rotation of the ventilation tube simultaneously creates a passage penetrating the substantially intact membrane and draws the ventilation tube through that passage.
2. Prior Art
Ventilation tubes are frequently implanted in or through the tympanic membrane to treat middle ear effusions by permitting ventilation, draining fluid discharge from the middle ear and allowing pressure equalization between the middle and outer ear. Various types of ear ventilation tubes, grommets, and similar prostheses are employed in such medical procedures and are manufactured in a wide variety of styles and designs particularly suited or adapted for specific purposes.
Conventionally, a ventilation tube was implanted by making a linear incision in the lower anterior quadrant of the tympanic membrane, draining excess fluid which had accumulated in the middle ear, and then inserting the leading end of the ventilation tube through the incision. Because the body of the ventilation tube is usually cylindrical and the incision is straight, and further because the leading end of the ventilation tube frequently incorporates an enlarged flange or projection, the incision occasionally permits premature extrusion or dislocation of the ventilation tube.
Incisions that were too large or too small would result in dislodged ventilation tubes, tearing of the tympanic membrane, or incisions that would not heal properly, thus requiring subsequent surgical repair or reconstruction. Since the ventilation tube was placed through the incision using forceps, obtaining the proper positioning and orientation of the ventilation tube within a restricted ear canal could be difficult. In some cases, the ventilation tube could be accidentally pushed entirely into the middle ear and released, requiring a surgical procedure for removal.
More recently, methods for implanting ventilation tubes have been developed which are designed to reduce or eliminate the initial incision. Modified ventilation tubes have been specifically developed to work in cooperation with these methods of implantation.
One representative example is U.S. Pat. No. 3,807,409 to Paparella, which discloses a medical ventilation tube having a notched inner or leading flange which permits one tapered edge to be inserted through an initial incision in the tympanic membrane, and then by rotating the body of the ventilation tube until the entire leading flange traverses from the outer side to the inner side of the membrane. This procedure permits an incision that is smaller than the maximum diameter of the inner flange without intentionally stretching the tympanic membrane, although the incision must still be larger than the body of the ventilation tube between the inner and outer flanges. Paparella '409 also discloses a rearwardly projecting flexible tab designed to facilitate the use of forceps in a nearly closed position, thus permitting increased access in a restricted ear canal, but decreasing the accuracy and precision with which the ventilation tube can be positioned or oriented.
U.S. Pat. No. 5,026,378 to Goldsmith discloses a method for implanting a ventilation tube in which the ventilation tube is mounted on a trocar that extends through the central bore or lumen of the ventilation tube and has a pointed distal tip. The distal tip is used to puncture the tympanic membrane by direct pressure exerted from the trocar on the membrane, and the truncated conical leading flange of the resilient ventilation tube is then forced through the aperture created by the distal tip of the trocar. The rear face of the ventilation tube abuts a sleeve which circumscribes the trocar and is attached to the myringotomy instrument. Manually retracting the trocar through the ventilation tube and sheath detaches the ventilation tube from the trocar and instrument. Goldsmith '378 further discloses providing the distal tip of the trocar with blades that extend directly rearward from the pointed tip to approximately one third the length of the conical region, and which assist in puncturing the membrane along predetermined lines to minimize the extent to which the membrane will tear along jagged edges or produce a non-uniform incision.
While Goldsmith '378 discloses a truncated conical leading flange that is generally coplanar with the outer surface of the conical distal tip (with the two surfaces being sufficiently proximate to one another so as to practically form continuations of one another), one important drawback of Goldsmith '378 is that the leading flange of the ventilation tube is substantially greater in diameter than the diameter of the trocar, thus increasing the likelihood that the membrane will tear jaggedly or produce a non-uniform incision that may not heal properly.
Significant pressure must be exerted directly on the tympanic membrane in order to stretch the incision sufficiently to insert the leading flange of the ventilation tube. This increased axial pressure can distort the tympanic membrane to the point where the membrane or trocar are dangerously close to or actually contact the delicate structures of the middle or rarely the inner ear, which are sometimes disposed as little as 2 mm from the normal plane of the membrane.
Another significant disadvantage of the Goldsmith '378 apparatus is that the distal tip of the trocar can slide along the tympanic membrane or become displaced from the most advantageous location for the ventilation tube as pressure is exerted on the trocar to puncture the membrane, particularly in the lower quadrant of the membrane where the angle between the membrane and the ear canal diverge the farthest. Consequently, ventilation tubes must frequently be implanted in less desirable or suitable quadrants of the tympanic membrane when using the Goldsmith '378 method, so that the trocar may be maintained as perpendicular as possible to the plane of the membrane without excess slippage.
Other representative examples in which a trocar or needle on which the ventilation tube is mounted is used to initially pierce the membrane are shown in U.S. Pat. Nos. 3,913,584 to Walchle; 3,530,860 to Majoros; and 3,888,258 and 3,948,271 to Akiyama. In addition, U.S. Pat. No. 3,645,268 to Capote discloses a ventilation tube having an open spearhead-shaped tip for piercing the membrane which remains connected to the ventilation tube within the middle ear subsequent to implantation of the ventilation tube.